1. Field of the Invention
The present invention relates to a method of manufacturing all-bent spring elements and, more particularly, tangential expanders for oil control plate-type piston rings by the method of plastic deformation.
2. Description of the Prior Art
Known in the prior art is a method of manufacturing tangential expanders of all-bent construction for plate-type oil control piston rings (French Pat. No. 1,529,788, Cl.B210) including the following operations:
coiling a serpentine blank from round wire; PA1 flattening the round wire serpentine blank into a rectangular wire serpentine blank; PA1 extruding thrust shoulders and stiffener ribs in the rectangular wire serpentine blank; PA1 calibrating for width the serpentine blank with extruded thrust shoulders and stiffener ribs; and PA1 bending the calibrated serpentine blank into an U-shaped profile.
The disadvantages of the known method of manufacturing all-bent tangential expanders are that, in the first place the flattening of the serpentine blank made from round wire is a labor-consuming operation, because it requires preliminary annealing of the blank in order to relieve internal stresses after bending the round wire into a serpentine blank; and for intermediate annealing operations following each intermediate flattening pass there must be not less than two. Otherwise the blank may become cracked since the extent of deformation is sufficiently large. The wire is anisotropic from the viewpoint of its mechanical properties; therefore, the flattening deformation must be strictly directional and combined with fixing the pitch which is highly problematic in practice. Otherwise the blank may have local overflows and distortions due to non-uniformity of hardening.
The entire process of flattening including intermediate annealing should take place with the compressed serpentine blank which is extremely difficult. Besides, extrusion of the thrust shoulders followed by calibration of the serpentine blank for width is a very labor-consuming operation for the same reasons as flattening. In addition, it should be borne in mind that the height of the thrust shoulders should be made with a high degree of accuracy (to about 0.05 mm).